In recent years, a technique called OpenFlow has been proposed. The OpenFlow is disclosed in Non Patent Literatures (NPLs) 1 and 2 and Patent Literatures (PTLs) 1 and 2. In the OpenFlow, a communication method between an OpenFlow switch (OFS) function and an OpenFlow controller (OFC), which is a control apparatus for the OFS function, is defined. These OFS and OFC are connected to each other via a control path called a secure channel. In addition, the OFS is controlled by a single OFC.
The OFS includes a flow table. In the flow table, at least a header field for identifying the flow of a packet and a process corresponding to the packet are paired and registered as an entry. The header field for identifying a packet is also referred to as a matching rule. The header field is formed by a plurality of tuples, and a wildcard can be designated for each tuple. By designating a wildcard, a flow range can be represented as a union. For example, it is possible to designate only the source IP (Internet Protocol) address in the header field of a certain entry and to set wildcards in the other tuples. In such case, the set entry represents a union of all flows transmitted from the designated IP address. Namely, all the packets transmitted from the designated IP address correspond to the set entry, irrespective of the destinations of the packets.
In addition, the process corresponding to a packet is also referred to as an action. Examples of the action include at least forwarding to a designated port, forwarding to the OFC, forwarding back to an ingress port, and discarding. Forwarding to a designated port is used for forwarding a packet to a switch at the next hop. Forwarding to the OFC is mainly used for querying a packet processing method.
When receiving a packet, first, the OFS searches the flow table. If an entry matching the incoming packet exists, the OFS processes the packet, in accordance with an action in the matched entry. Since a priority can be set in an entry, if a packet matches a plurality of entries, the OFS uses an action in an entry with the highest priority.
If the flow table does not include any entries matching the incoming packet, the OFS queries the OFC for a process to be executed on the incoming packet. In such case, the OFS forwards part of the packet or the entire packet to the OFC via the secure channel. After receiving the query, as needed, the OFC adds an entry in the flow table and notifies the OFS of a processing method.
In addition, PTLs 3 and 4 disclose a network architecture including: a control apparatus that has a control function; and a switch that has a forwarding function and that is controlled by the control apparatus.    PTL 1:    Japanese Patent Kokai Publication No. JP2011-082834A    PTL 2:    Japanese Patent Kokai Publication No. JP2011-101245A    PTL 3:    Japanese Patent Kokai Publication No. JP2006-135971A    PTL 4:    Japanese Patent Kokai Publication No. JP2006-135975A
NPL 1:
Nick McKeown, and seven others, “OpenFlow: Enabling Innovation in Campus Networks,” [Searched on Jun. 28, 2011], Internet <URL: http://www.openflowswitch.org/documents/openflow-wp-latest.pdf>
NPL 2:
“OpenFlow Switch Specification Version 1.1.0 (Wire Protocol 0x01),” Dec. 31, 2009, [Searched on Feb. 16, 2012], Internet <URL: http://www.openflowswitch.org/documents/openflow-spec-vp1.1.0.pdf>